Making mitered corners on large casework is not a simple task. Especially if you don’t have a sliding table saw or a high quality track saw. Long and wide boards are hard to maneuver or hold pressed against the saw table. They are also always cupped, twisted, etc. (I know, it just keeps happening to me!) which causes curved cut line. This is a jig that I made for such situations:

It is a plywood 45 deg. wedge with guide rail. First, I cut miter using table saw (or by hand) slightly oversized (~1 mm) and clamp the jig to the board like this:

I hold the router slightly turned with one handle closer to me and one extended for better tipping control.The jig is very rigid and will straighten up the board if the latter is slightly cupped. I use spiral bit for smoother operation. Since a relatively large area of end grain is cut you will be able to remove small amount of material at a time and several passes will be required until router base glides along the guide rail. An added benefit is that your final cut will be exactly along the edge of the jig. You can literally split a thin pencil line. The surface of the cut is perfectly flat, straight and smooth. I usually scribe a line on the left edge of the board where router bit exits the cut (left side) to prevent tearouts. This is how the finished miter looks:

A more perfectest miter can not be made by any craft known to man :-)

And even if you own one of those fancy Euro sliders you can find this jig useful for feeding your cattle:

Great jig. I love it and I’m going to try it. Are you repositioning the jig to control how much material you take off or just freehanding the router (away from the fence) to hog off most of the material before the final pass? I think using shims between the router base and the fence may be a good method of controlling this. I need to build one. Thanks for passing this along.

David, I actually tried angled bits, but1) They don’t make bits this large. For a 20 mm (3/4”) stock it would have to be ~40 mm (1.6”) diameter V-bit. 2) What is sold as 90 deg. V-bits are not always 90 deg. by as much as 3-5 deg. It is not noticeable when cutting a groove, but in a miter it is very obvious. Don’t ask how I know.

Carpenterdon,Actually you’d need to make infinite number of these jigs for every angle. However, I only have 1, because furniture that I make tends to be rectangular.The angle on the jig is defined by little triangle brackets that hold two surfaces together. Those can be cut very accurately on a bench top saw. On the other hand it is nearly impossible to cut accurate 45 degree bevel across 6 feet long 1.5 feet wide board on a little saw, because the board is too heavy and unwieldy. Besides, the bevel made on this jig comes out perfect every time and this fits into my overall approach of doing more with less.Hope this answers your question.